1. Field of the Invention
The present invention relates generally to switching power regulator circuits, and more specifically, to a resonant switching power converter in which burst mode pulse patterns are varied between bursts.
2. Background of the Invention
In resonant switching power converters, as output current demand falls, the switching frequency is raised to reduce the power output. However, when low or zero-load conditions are encountered, the required switching frequency may become impractical and will typically cause a dramatic drop in efficiency due to increases in switching losses in conjunction with the relative drop in output power vs. the power consumed in ordinary switching operation. For the above reasons, a low-power “burst” mode is typically employed in low or zero output current demand periods, during which the output voltage is maintained by issuing a burst of pulses to restart oscillation of the resonant circuit at a level sufficient to re-charge the output capacitor of the resonant switching power converter. Between the bursts, the output capacitor supplies power to the load.
However, typical burst operation causes audible noise due to the bursts being infrequent enough to fall into the audible range. Due to magneto-restrictive behavior, cores of inductors and transformers will cause audible vibrations due to the transients generated by the bursts.
Therefore, it would be desirable to provide a resonant switching power converter with a low-power operating mode having reduced audible vibration.